"The calculation was simple enough. Thanks to the disfranchisement of blacks and the reign of terror that accompanied it, the South had become solidly Democratic by the beginning of the 20th century, the Deep South exclusively so. One-party rule translated into outsize power on Capitol Hill: when Roosevelt took office, Southerners held almost half the Democrats’ Congressional seats and many of the key committee chairmanships. So whatever Roosevelt wanted to put into law had to have Southern approval. And he wouldn’t get it if he dared to challenge the region’s racial order."
Kevin Boyle in The New York Times reviews Ira Katznelson's Fear Itself: The New Deal and the Origins of Our Time.